The invention pertains to telecommunications and, more particularly, with the detection of flags used to identify packets of information sent on telecommunication channels.
Packet transmission is a technique used to efficiently send digitized data and voice through telecommunication channels. Under standards adopted in Europe and the United States (e.g., X.25) each packet starts and ends with the eight bit flag "01111110." If a channel is idle, flags are sent each 0.45 second. If a channel is disabled, all "1's" will be received.
It is known to monitor a channel for flags so that appropriate measures may be taken if a channel becomes disabled. For example, the Intel Corporation's Model 8273 programmable HDLC/SDLC protocol integrated circuit may be used for this purpose.
The use of specialized integrated circuits requires a relatively large hardware and software effort. The Intel 8273 integrated circuit is, for example, intended for use with Intel's 8080 or 8085 microprocessor so hardware deviations require substantial design effort.
It is desirable to provide a circuit which is compatible with existing systems without extensive additional hardware or software changes.